Aurora A activates D-TACC–Msps complexes exclusively at centrosomes to stabilize centrosomal microtubules

Teresa P Barros,Anthony A Hyman,Kazuhisa Kinoshita,Jordan W Raff

doi:10.1083/jcb.200504097

Abstract

Centrosomes are the dominant sites of microtubule (MT) assembly during mitosis in animal cells, but it is unclear how this is achieved. Transforming acidic coiled coil (TACC) proteins stabilize MTs during mitosis by recruiting Minispindles (Msps)/XMAP215 proteins to centrosomes. TACC proteins can be phosphorylated in vitro by Aurora A kinases, but the significance of this remains unclear. We show that Drosophila melanogaster TACC (D-TACC) is phosphorylated on Ser863 exclusively at centrosomes during mitosis in an Aurora A–dependent manner. In embryos expressing only a mutant form of D-TACC that cannot be phosphorylated on Ser863 (GFP-S863L), spindle MTs are partially destabilized, whereas astral MTs are dramatically destabilized. GFP-S863L is concentrated at centrosomes and recruits Msps there but cannot associate with the minus ends of MTs. We propose that the centrosomal phosphorylation of D-TACC on Ser863 allows D-TACC–Msps complexes to stabilize the minus ends of centrosome-associated MTs. This may explain why centrosomes are such dominant sites of MT assembly during mitosis.

Highlights

The centrosome is the main microtubule (MT) organizing center in animal cells, and it plays an important part in organizing many processes in the cell, including cell polarity, intracellular transport, and cell division (Glover et al, 1993)
We find that D-Transforming acidic coiled coil (TACC) phosphorylated on this site (P–Drosophila melanogaster TACC (D-TACC)) is only detectable at centrosomes, whereas nonphosphorylated D-TACC, like most other centrosomal proteins, has large pools of protein that are present in the cytoplasm of D. melanogaster embryos
As Ser863 is a conserved site of Aurora A phosphorylation in vitro, it seems likely that Aurora A directly phosphorylates Ser863 in vivo, we cannot exclude the possibility that Aurora A indirectly stimulates the phosphorylation of Ser863 at centrosomes by activating another kinase. It is unclear why Aurora A only stimulates the phosphorylation of D-TACC at centrosomes, but we note that two activators of Aurora A kinase, TPX2 and Ajuba, are themselves concentrated at centrosomes (Hirota et al, 2003; Tsai et al, 2003)

Summary

Introduction

The centrosome is the main microtubule (MT) organizing center in animal cells, and it plays an important part in organizing many processes in the cell, including cell polarity, intracellular transport, and cell division (Glover et al, 1993). Aurora A protein kinases are centrosomal proteins that are essential for mitosis and have been widely implicated in human cancer (Meraldi et al, 2004; Marumoto et al, 2005). They have several functions in mitosis, and they appear to play a important part in regulating centrosome behavior. They are, for example, required for the dramatic recruitment of pericentriolar material to the centrosome, which occurs as cells enter mitosis (Hannak et al, 2001; Berdnik and Knoblich, 2002). In Xenopus laevis egg extracts, for example, the balance of activity between XMAP215 and the MT-destabilizing protein XKCM1/MCAK (mitotic centromere-associated kinesin) at MT plus ends seems to be the main parameter that determines the overall stability of MTs (Tournebize et al, 2000; Kinoshita et al, 2001)

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